1. Field of the Invention
The present invention relates to a syringe pump for injecting various drug solution, blood, or the like to human bodies using a syringe.
2. Description of the Related Art
FIG. 1 shows a first related art of the syringe pump (JP, B2, 63-44389). The syringe pump 11 of the first related art includes an operation/display section 13 which is an upper surface portion of a case 12, and a syringe attaching section 14. The operation/display section 13 has various operation buttons and display sections, and the syringe attaching section 14 has a flange attaching section 15, a barrel attaching section 16, a slider 17 and a syringe diameter detecting section 18. The barrel attaching section 16 has a pair of projected ribs 21 which form a groove shaped section.
The flange attaching section 15 has end surfaces 21a of the pair of projected ribs 21 on a side of the slider 17, a pair of projected portions 22 opposed to the end surfaces 21a, and slits 23 between the end surfaces 21a and the projected portions 22. In order to use the syringe pump 11, the syringe 24 which is loaded with drug solution or the like is attached to the syringe attaching section 14. At the time of the attachment, a barrel 25 of the syringe 24 is attached to the barrel attaching section 16 and the syringe diameter detecting section 18, a flange section 26 of the barrel 25 is inserted into the slits 23, and a flange section 28 of a plunger 27 is attached to the slider 17.
The syringes 24 are manufactured by a plurality of manufacturers, and one manufacturer manufactures the syringes 24 of plural types. Dimensions of the respective sections of the syringe 24 differ according to manufacturers and types of the syringes 24, and a thickness of the flange section 26 of the barrel 25 also differs according to manufacturers and types of the syringes 24. Meanwhile, the syringe pump 11 is designed so as to be capable of being used for the syringes 24 of all manufacturers and all the types. A width of the slits 23 is, therefore, determined so that the most thick flange section 26 in the syringes 24 of various manufacturers and types can be inserted thereinto.
A diameter of the barrel 25 also differs according to manufacturers and types of the syringes 24. Since the syringe diameter detecting section 18, however, detects the diameter of the barrel 25, a sliding speed of the slider 17 for obtaining a desired infusion speed is determined based on the detected diameter. The slider 17 slides to a direction approaching the flange attaching section 15 at the determined sliding speed so as to press the flange section 28 of the plunger 27, and the plunger 27 is gradually inserted into the barrel 25. As a result, the infusion is executed always at the desired infusion speed regardless of the diameter of the barrel 25.
When the slider 17 slides to a position corresponding to a state where a tip of the plunger 27 is separated from the end surfaces 21a by a predetermined distance, a “warning that shows predetermined time before end of infusion” is given. When the slider 17 further slides to a position corresponding to a state where the tip of the plunger 27 is separated from the end surfaces 21a by a distance for reaching an injection end of the barrel 25, an “infusion end warning” is given. That is to say, an infusion quantity is calculated at the time of the infusion on the premise that the flange section 26 comes in pressure contact with the end surfaces 21a. 
In a second related art of the syringe pump, an elastic supporting piece which elastically presses the flange section 26 of the barrel 25 of the syringe 24 against the end surfaces 21a is provided between the projected portions 22 in the syringe pump 11 of the first related art (JP, B2, 6-36827).
In the syringe pump 11 of the first related art, however, the width of the slits 23 is determined so that the flange section 26 which has the largest thickness in the syringes 24 of various manufacturers and types can be inserted thereinto. When the flange section 26 is inserted into the slits 23, therefore, a gap is normally generated between the slits 23 and the flange section 26.
When the slider 17 presses the plunger 27, the barrel 25 also moves to an opposite direction from the slider 17 in result until the flange section 26 comes in pressure contact with the end surfaces 21a. While the barrel 25 is moving, the infusion is not executed at all, or the infusion speed is lowered. Even if the moving distance of the barrel 25 is slight, when a slight quantity of highly medicable drug solution is infused or the like, the moving of the barrel 25 cannot be ignored.
On the contrary, in the syringe pump of the second related art, since the elastic supporting piece, which elastically presses the flange section 26 of the barrel 25 of the syringe 24 against the end surfaces 21a, is provided, when the flange section 26 is fitted between the elastic supporting piece and the end surfaces 21a, the flange section 26 comes in pressure contact with the end surfaces 21a. When the slider 17 presses the plunger 27, the barrel 25 does not move to the opposite direction from the slider 17.
In a state, however, in which the syringe 24 is attached to the syringe pump, since the plunger 27 of the syringe 24 is positioned above the elastic supporting piece, the elastic supporting piece should be necessarily shortened. Since the thin elastic supporting piece is easily damaged, the elastic supporting piece should be necessarily thicken, and in result it has strong elastic force. When the elastic supporting piece is short and has the strong elastic force, strong force should be applied to the elastic supporting piece in order to elastically deform it. In a state where the elastic supporting piece is not elastically deformed, the gap between the elastic supporting piece and the end surfaces 21a is extremely narrow.
The flange section 26 is, therefore, difficultly fitted between the elastic supporting piece and the end surfaces 21a, and even if the flange section 26 is not fitted therebetween, the flange section 26 is easily taken to be fitted by an operator. In the end, also in the syringe pump of the second related art, the barrel 25 frequently moves to the opposite direction from the slider 17 due to the pressing of the plunger 27 by the slider 17 until the flange section 26 comes in pressure contact with the end surfaces 21a. 
In any one of the syringe pumps 11 of the first and second related arts, at the time of attaching the syringe 24, even if the flange section 26 of the barrel 25 is not attached into the slits 23 which is the proper position but is attached to an improper position, for example, a position which is closer to the slider 17 than the projected portions 22 as shown by a chain line in FIG. 1, the attachment to the improper position is not detected at all. When the flange section 26 of the barrel 25 is attached to the position which is closer to the slider 17 than the projected portions 22 as shown by the chain line in FIG. 1, the flange section 28 of the plunger 27 is separated from the end surfaces 21a excessively in comparison with the case where the flange section 26 is attached into the slits 23.
When the flange section 28 of the plunger 27 is attached to the slider 17, it is necessary to excessively separate also the slider 17 from the end surfaces 21a. The syringe pump 11 judges to necessarily infuse a larger quantity of the drug solution than the quantity of the drug solution with which the syringe 24 is actually loaded, namely, judges to necessarily slide the slider 17 over a longer distance than the proper distance, and starts the infusion. As a result, before the “infusion end warning” is given, or in some cases even before the “warning that shows predetermined time before end of infusion” is given, the tip of the plunger 27 reaches the injection end of the barrel 25.
Meanwhile, the tip portion of the plunger 27 has a flexible sealing member made of rubber or the like in order to seal the solution. When the pressing of the plunger 27 by the slider 17 is continued also after the tip of the plunger 27 reaches the injection end of the barrel 25, the sealing member on the tip of the plunger 27 is compressed so as to be deformed. That is to say, while the sealing member is being compressed and is deformed, the plunger 27 is continued to be pressed by the slider 17. Since, however, the compressive deformation of the sealing member is limited, when the plunger 27 cannot be moved despite the pressing of the plunger 27 by the slider 17, the syringe pump 11 judges that the syringe 24 is blocked, so that “blocking warning” is given.
During time when the tip of the plunger 27 reaches the injection end of the barrel 25 and then the “blocking warning” is given, however, the infusion is actually not executed at all. Even if, therefore, the syringe 24 is replaced immediately upon the “blocking warning”, the infusion is regarded to be interrupted. When the infusion is interrupted while the solution is being infused in order to inject a slight quantity of vasopressor, hypotensor or the like, the interruption of the infusion is serious such that this determines life and death of a patient. Even when the interruption of the infusion is not so serious, the operator gets confused in the following case. The case is such that the infusion is actually completed before the “warning that shows predetermined time before end of infusion” or the “infusion end warning” is given, and that althougt the syringe 24 is not actually blocked, the “blocking warning” is given.